This invention relates to a method of detecting the opening of a throttle valve in a fully closed position in an internal combustion engine, which can detect the valve opening in an accurate manner.
In fuel supply control for internal combustion engines, it is required to determine with accuracy whether or not the throttle valve is actually in a fully closed position when the engine is in a decelerating condition for instance. To this end, Japanese Provisional Patent Publication No. 58-206835 has been proposed, which comprises detecting whether or not the throttle valve is in a substantially fully closed position, determining that the engine is in a decelerating condition when the throttle valve is determined to be in the substantially fully closed position and at the same time the engine speed is decreasing toward an idling speed, and interrupting the fuel supply to the engine to thereby improve the emission characteristic and fuel economy of the engine.
To ascertain whether or not the throttle valve is in a fully closed position, it is already known to determine whether or not a throttle opening value detected by a throttle opening sensor, which may be connected to the valve shaft of the throttle valve, e.g. a potentiometer, is smaller than or equal to a fully closed position-discriminating value which is the sum of a fully closed position-indicative value stored beforehand and a predetermined value. However, the actual position of the fully closed throttle valve can differ between individual throttle valves, and also vary with aging, e.g. mounting tolerances of the throttle valve and the throttle opening sensor, adhesion of dust or carbon to the throttle valve, and wear of component parts of the throttle valve.
Therefore, if a fixed value is used as the fully closed position-discriminating value, disadvantageously the throttle valve can wrongly be determined to be in a position other than the fully closed position though the valve is actually fully closed, due to aging change in the actual fully closed position of the throttle valve or a like cause. In order to ensure accurate detection of the fully closed position of the throttle valve, a method has been proposed by U.S. Pat. No. 4,359,894 wherein the smallest one of detected values of the throttle valve opening is stored, and when a newly detected value is smaller than the presently stored smallest value, the former is stored as the up-to-date smallest value. Further, a method has also been proposed by U.S. Ser. No. 456,605 filed Jan. 10, 1984, now U.S. Pat. No. 4,515,009 wherein a detected value of the throttle valve opening is newly stored as the smallest value in place of the presently stored smallest value only when the detected value keeps the same value smaller than the presently stored smallest value over a predetermined period of time, so as to avoid erroneous updating of the smallest stored value due to noise or other disturbances.
On the other hand, when a load creating equipment such as an air conditioner is operated to apply a load on the engine during idling operation, the resulting increased engine load can cause a drop in the engine speed, making the engine operation unstable. To overcome this disadvantage, it has been proposed, e.g. by Japanese Utility Model Publication No. 47-38678 and Japanese Provisional Patent Publication No. 50-70740, to forcedly open the throttle valve to a required degree during operation of the load creating equipment, to thereby increase the quantity of intake air for the engine for prevention of a decrease in the idling speed.
Further, an engine control method has been proposed by Japanese Utility Model Publication No. 55-10595, which is adapted to forcedly open the throttle valve to a required degree at restarting of the engine in a hot condition until the engine temperature drops below a predetermined value, so as to eliminate vapor lock badly affecting the startability and driveability of the engine.
According to these proposed methods, the phenomenon can occur that the throttle valve is forcedly opened upon starting of the engine, depending upon the operative state of the air conditioner or the engine temperature, and then the valve is kept open. On such occasion, if any of the proposed methods for detecting the fully closed throttle valve position is executed, the valve opening degree of the forcedly opened throttle valve then assumed can be wrongly regarded as the actual throttle opening value indicative of the fully closed position, and then stored as the smallest value. If such erroneous value is stored, a throttle opening value detected thereafter will then be smaller than the fully closed position-discriminating value set by the use of the erroneously stored value when the load creating equipment is at rest, for instance, causing a wrong diagnosis that the engine is in a decelerating condition, to interrupt the fuel supply to the engine, even when the engine is actually not in a decelerating condition.